One design criterion for a circuit breaker holds that upon occurrence of a load fault which creates an unacceptably large current draw (e.g., a short circuit current) through closed contacts of a circuit breaker, the circuit breaker mechanism must open the contacts in a manner that promptly terminates the current. Certain known circuit breakers that employ one or more pivotally mounted contact arms utilize electromagnetic blow-apart, or blow-open, force to blow open the contact arm(s) upon the occurrence of such a sudden load fault. Although the blow-open force quickly initiates contact arm motion to begin tripping the circuit breaker, current may continue to arc across the contacts as the contact arm(s) swing open. Consequently, further circuit breaker design principles include minimizing (and ideally eliminating) such arcing as the tripping continues. Furthermore, once current flow has terminated, any opportunity for its re-establishment must be foreclosed as the tripping concludes.
In accomplishing prompt arrest of current arcing across blowing-open contacts, it may be desirable for the circuit breaker mechanism to augment the impetus of the blow-open force as the tripping continues toward conclusion. But in doing so, the mechanism's augmentation of the force acting on the swinging contact arm(s) must not induce rebound of the contact arm(s) off of a stop to an extent that could potentially re-establish current flow.
Consider for example a circuit breaker that employs a spring-loaded, over-center toggle mechanism which goes over-center during the trip. As the mechanism goes over-center, an operating spring which had been effectively applying to the contact arm(s), a force resisting, but not preventing, the trip, now suddenly applies its force to aid the trip, driving the swinging contact arm(s) against the stop. That added force must not cause excessive contact arm rebound from the stop.
Circuit breaker design must therefore take into consideration various factors that may conflict. A better circuit breaker design will account for such factors to provide a circuit breaker that will terminate a specified fault current within a specified response time, with better assurance that current will not be re-established once the circuit breaker has been tripped. Moreover, a successful circuit breaker design should be cost and space efficient.
It is toward these and other objectives that the present invention is directed.
Thermal and magnetic trip actuators are also important considerations in successful circuit breaker design, especially where either one or both apply actuating force to a trip mechanism during a trip. A circuit breaker design should efficiently integrate magnetic and thermal trip actuators with each other, with the trip mechanism, and with other associated components of the circuit breaker mechanism. The present invention relates to an integration of both thermal and magnetic trip actuators in a circuit breaker.
Accordingly, one aspect of the present invention relates to a circuit breaker comprising a contact member that forms a portion of an interruptable load current path through the circuit breaker, an operating mechanism for selectively positioning the contact member to a circuit-making position and to a circuit-breaking position, the contact member being movable along a range of non-circuit-making positions between the circuit-making position and the circuit-breaking position, a first trip actuator for detecting a fault condition, a second trip actuator for detecting a fault condition, a latch for releasably latching the operating mechanism in latched condition when the operating mechanism positions the contact member in circuit-making position, a trip mechanism that is responsive to the two trip actuators and acts via the latch to release the operating mechanism from latched condition and thereby allow the contact member to move to circuit-breaking position upon occurrence of a fault detected by either one of the trip actuators, the trip mechanism comprising, a plunger, a plunger guide for guiding motion of the plunger along a path of travel, and a coupling that couples motion of the plunger to the latch for releasing the operating mechanism from latched condition upon detection of a fault by either one of the trip actuators, one of the trip actuators comprising a thermally responsive member for causing motion of the plunger upon detection of a fault, the other of the trip actuators comprising a magnetically responsive member for causing motion of the plunger upon detection of a fault, and wherein each trip actuator is capable of moving the plunger independently of the other trip actuator to cause release of the operating mechanism from latched condition in response to detection of either a thermal fault or a magnetic fault.
Another aspect of the invention relates to a trip mechanism comprising a first trip actuator for detecting a fault condition, a second trip actuator for detecting a fault condition, a plunger, a plunger guide for guiding motion of the plunger along a path of travel, one of the trip actuators comprising a thermally responsive member for causing motion of the plunger upon detection of a fault, the other of the trip actuators comprising a magnetically responsive member for causing motion of the plunger upon detection of a fault, and wherein each trip actuator is capable of moving the plunger independently of the other trip actuator to cause the trip mechanism to trip in response to detection of either a thermal fault or a magnetic fault.
The foregoing, along with further features, advantages, and benefits of the invention, will be seen in the ensuing description and claims, which are accompanied by drawings. The description and drawings disclose a presently preferred embodiment of the invention according to the best mode contemplated at this time for carrying out the invention.